Nova Scotia watersheds recovering from decades of acid rain
Paul Withers | CBC | Posted: November 2, 2017 9:00 AM | Last Updated: November 2, 2017
'Enormous challenge' for water utilities, says Dalhousie University expert
Lakes damaged by acid rain are coming back to life in Nova Scotia faster than anyone expected — and the recovery has added expenses for Halifax Water.
As acid levels in the lakes drop, there's an increase in the number of organisms, like algae, that are in the water. That means more chemicals are needed to remove organic matter from lake reservoirs to make the water safe to drink. The cost of the chemicals is escalating by $400,000 yearly, according to Halifax Water.
"It's created enormous challenges from the standpoint of water utilities, particularly utilities like Halifax Water that are used to treating lakes that have been acidified," said Graham Gagnon, director of the Dalhousie University Centre for Water Resources Studies.
Halifax lake sulphates down
Gagnon's research indicates stricter sulphur dioxide emission standards and the closure of coal plants in the U.S. and Canada have had a dramatic effect on watersheds in Nova Scotia.
Because of prevailing winds, the province has been described as the end of the tailpipe for some pollutants.
"Aquatic life is coming back," said Gagnon.
Sulphate concentrations dropped by 52 per cent in Lake Major between 1999 and 2015, and by 38 per cent in Pockwock Lake, according to a 2016 paper by Dalhousie University's Lindsay Anderson that's published in the journal Environmental Science and Technology.
Lake Major and Pockwock Lake are the sources of drinking water for most of Halifax. Both are isolated and free from waste water or industrial or agricultural discharges.
Gagnon calls that a "significant reduction."
Improvements in pH levels
One of the gauges of lake health are pH levels, which measure alkalinity. The lower the pH, the higher the acidity.
In 2002, the pH level was below five for 153 days at Lake Major, according to the Anderson paper. From 2010 to 2015, it measured below five for just 10 days.
In 2005, the pH at Pockwock Lake was under five for 162 days. Between 2010 and 2015, pH was below five on just seven days.
Added costs
Halifax Water said the changing water quality requires more testing, monitoring and chemicals.
"Are we happy there is less acid rain in Nova Scotia and Atlantic Canada? Yes we are. Are there side-effects of that? There sure are, and we are dealing with it," said Halifax Water spokesperson James Campbell.
This year, Halifax Water issued a request for proposals that forecast its treatment plant at Lake Major in Dartmouth would use 1,000 kilograms a day of the coagulant aluminium sulphate to clot organic matter.
Gagnon estimates Lake Major now uses five times more coagulant and Pockwock twice as much since the lakes have recovered.
The filtering process is producing correspondingly large amounts of alum sludge that is dried in two large holding pits behind the Lake Major plant before it is hauled off site for disposal.
The plant's filters were not designed for current volumes. Campbell said Halifax Water has had to flush the filters more often because they get jammed, and it has installed a system to scour the filters more often. That's an added expense, too, he said.
Increased algal activity
Gagnon said he tuned in to lake recovery in 2012 when some people in Halifax and Bedford noticed an earthy, musty taste and odour in their tap water.
It was geosmin, a non-toxic chemical produced by algae and soil-based bacteria.
In 2012, geosmin showed up for the first time ever in Pockwock Lake, which supplies drinking water for the Halifax side of the municipality.
"It's an indicator of algal activity. We couldn't understand why it was there. We thought maybe it's just an anomaly," said Gagnon. "But each year, it comes back. Every fall we smell a slightly different odour."
Lake bottom sediment clues
Gagnon and the team at Dal are working to date the sediment at the bottom of Lake Major and Pockwock Lake. They are looking for aquatic life that existed in the lakes before the arrival of acid rain.
"We want to know what kind of carbon level was there and from that we can kind of know where is our ceiling — where is the lake potentially going?" he said. "I say potentially because in the 1800s the planet was cooler. If you have a warmer planet, aquatic species can multiply more rapidly. So it gives a clue, but it doesn't give us a final answer."
Climate change complications
Gagnon and his team at Dalhousie are also trying to sort out how to redesign the plants for the future.
He believes warmer temperatures from climate change have likely acted as an accelerator, serving as an incubator for the algal blooms that have accompanied the lake recovery.
"Certainly if we look at the research from the '80s, the idea of lake recovery was a very long period, not a short period. It tells me climate change is really shortening this recovering period where we get back to a more fertile lake system," said Gagnon.
Halifax Water says the treatment plants and operators have to adjust to changing water quality.
"Those are costs we will incur. It's not a matter of, 'We are not going to absorb those costs, we are not going to pass on those costs, we are not going to have those costs.' The water quality has to be what it is," said Campbell.